High-capacity packet-switched network

ABSTRACT

A packet-switched WDMA ring network has an architecture utilizing packet stacking and unstacking for enabling nodes to access the entire link capacity by transmitting and receiving packets on available wavelengths. Packets are added and dropped from the ring by optical switches. A flexible credit-based MAC protocol along with an admission algorithm enhance the network throughput capacity.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 11/480,605 filed on Jul. 3, 2006, (currently allowed) which isa continuation of U.S. patent application Ser. No. 09/940,034 filed onAug. 27, 2001, entitled “HIGH-CAPACITY PACKET-SWITCHED RING NETWORK”(now U.S. Pat. No. 7,085,494). Application Ser. No. 09/940,034 alsoclaims priority from U.S. Provisional Patent Application Nos.60/239,766, filed on Oct. 12, 2000 and 60/240,464, filed on Oct. 13,2000. Each of the above cited applications is incorporated herein byreference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

FIELD OF THE INVENTION

The present invention relates generally to communication systems and,more particularly, to optical communication networks.

BACKGROUND OF THE INVENTION

As is known in the art, an optical ring network includes a plurality ofnodes connected by an optical fiber so as to form a ring thatinterconnects each of the nodes. Ring networks can include a pluralityof fiber rings for network protection. Regional access networks withring topologies are attractive because they easily recover from a singlefailure. Also, ring networks allow simple synchronization ofgeographically distant nodes. Media Access Control (MAC) protocols inring networks ensure that nodes receive their negotiated bandwidths. Anew bandwidth demand is accommodated depending on the availableresources and applied MAC protocol. In single-channel ring networkswhere nodes operate at the aggregate link bit-rate, the admissioncontrol is relatively straightforward. For example, in the FiberDistributed Data Interface (FDDI) protocol, the sum of all requestedbit-rates should be less than the link bit-rate. In MAC protocols withspatial re-use, the sum of requested bit-rates passing through any linkshould be less than the link bit-rate.

However, with development of Wavelength Division Multiple Access (WDMA)technology, the total throughput of a packet-switched ring network canbe significantly increased. Existing network architectures and protocolsmay not be able to utilize the enhanced throughput provided by WDMAtechnology.

It would, therefore, be desirable to provide an architecture for a WDMApacket-switched ring network that enhances the data throughput capacity.It would further be desirable to provide a MAC protocol for the novelarchitecture of the present invention. It would also be desirable toprovide an admission algorithm to operate in conjunction with a MACprotocol for a high capacity packet-switched ring network.

SUMMARY OF THE INVENTION

The present invention provides an optical packet-switched ring networkutilizing WDMA technology with enhanced throughput capacity. In oneaspect of the invention, an optical packet-switched ring networkincludes an architecture in which each node has an optical switch, suchas a 2×2 switch, connected to the ring fiber. A transmit switch, whichcan include a packet buffer, is connected to the optical switch. Awavelength stacking system stacks packets on multiple wavelengths toform a composite packet, which is provided to the transmit switch. Apacket is added to the ring network when the transmit switch and theoptical switch are set to the cross state.

In one embodiment, the wavelength stacking system includes a tunablelaser coupled to a wavelength demultiplexer via a circulator. Delaylines and a reflector coupled to the demultiplexer operate to delay eachwavelength by respective time slot multiples for alignment in time,i.e., stacked in wavelength.

The node can further include a buffering receive switch coupled to theoptical switch for dropping packets from the ring network. A wavelengthunstacking system is coupled to the receive switch for unstackingreceived packets. A packet is received when the optical switch and thereceive switch are set to the cross state.

In a further aspect of the invention, a credit-based MAC protocol isprovided for a packet-switched ring network. Nodes renew creditallocations one per frame period. Counters for each source-destinationpair are loaded with a negotiated number of credits. Only queues withpositive counter values can make a reservation. The frame ends when eachqueue is empty or is out of credits or frame length is reached.

In another aspect of the invention, a network includes an admissioncontroller for determining whether bandwidth requests can be allocatedto the corresponding source-destination pair. In one embodiment, theadmission controller calculates whether the MAC protocol ensures apredetermined number of credits to the source-destination node pair ineach frame for the existing credit allocation.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a schematic representation of a high-capacity opticalpacket-switched ring network in accordance with the present invention;

FIG. 2 is a schematic representation showing further details of thenetwork of FIG. 1;

FIG. 3 is a timing diagram for a high-capacity optical packet-switchedring network in accordance with the present invention;

FIG. 4 is a schematic diagram of one embodiment of a transmit (receive)switch that can form a part of a high-capacity optical packet-switchedring network in accordance with the present invention; and

FIG. 5 is a schematic block diagram of a ring network architectureintegrating multiple data services in accordance with the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an exemplary ring network 100 having an architecture thatenhances the throughput of high-capacity packet-switched ring networksin accordance with the present invention. In general, network nodesNa-Nn access the entire link capacity by transmitting and receivingpackets in parallel on all available wavelengths. Packets are added anddropped from the ring by optical switches, which avoid the need forproblematic fast tunable receivers. The bandwidth allocation of thenetwork is more flexible than in networks having fixed tuned or slowtunable receivers. In one embodiment, a MAC protocol for thepacket-switched ring network is based on credits and a dynamic admissioncontrol algorithm requires minimal processing complexity and can followfast traffic changes.

FIG. 2 shows further details of an exemplary node 200 of a WDMApacket-switched ring network 100 in accordance with the presentinvention. The network architecture is based upon “wavelength stacking,”which is described in U.S. Provisional Patent Application No.60/240,464, filed on Oct. 13, 2000. In general, time is divided intoslots of duration T_(p) with a control channel CC used for network andpacket management. A composite (multi-wavelength) packet is created by afast tunable laser 202 in contiguous time slots at W, e.g., three (λa,λb, λc), different wavelengths. The composite packet is directed by acirculator 204 to a wavelength demultiplexer 206 followed by a bank ofdelay lines 208 and a reflector 210. The different wavelength componentsλa, λb, λc are delayed by multiples of T_(p) so that they are aligned intime and “stacked” in wavelength.

The wavelength-stacked packet is directed from the circulator 204 to atransmit switch T, which can include a packet buffer TB, to the input ofan optical switch S, which can be provided as a 2×2 switch. A receiveswitch R provides packets from the optical switch S to a receivecirculator 214. The received packet is unstacked through a wavelengthdemultiplexer 206 and reflector 210, which can be the same demultiplexerand reflector used on the transmit side, and a bank of delay lines 212.A detector 216, such as a photodiode, is used to extract data from theunstacked packets.

The optical switch S operates in conjunction with the transmit andreceive switches T, R to add and drop packets from the ring network.More particularly, the transmit switch T stores a packet that has beenstacked, but not yet transmitted, while another packet is being stacked.The receive switch R stores a packet that has arrived, while anotherpacket is being unstacked. By using the optical switch S for packettransmissions and receptions, the need for relatively problematic fasttunable receivers is avoided. With this arrangement, the MAC protocoland admission control algorithm are significantly simplified withrespect to the network where wavelengths are pre-allocated to thereceivers and accessed individually, as described more fully below. TheMAC/admission simplification occurs since traffic is balanced overwavelengths at the physical layer rather than at higher layers (by theMAC and admission control protocols).

FIG. 3 shows an exemplary timing diagram for a three (W=3) wavelengthpacket. In general, because wavelength stacking takes W time slots toeffect, a node must decide in advance when to access the medium. Aseparate wavelength is used as a control channel CC for the advancedreservations. Time slots 300 are grouped into cycles 302 of length W,which is shown as three cycles (W=3). Each node can transmit and receiveat most one packet within each cycle 302 to facilitate packet stackingand unstacking. A node listens to the control channel and stores thechosen destinations in a potentially empty slot of the currentreservation cycle. The node reserves some of the remaining destinationsnot been chosen in the current cycle for which it has packets and unusedcredits. The destination node deletes the reservation made for it, andpossibly makes a new reservation.

The timing diagram shows packet transmission and reception for a givennode i in the ring network, such as the ring network 100 shown in FIGS.1 and 2. Whenever node i reserves a time slot TS0, the node tunablelaser 202 (FIG. 2) starts transmission at the beginning of the nextcycle C1. Wavelength stacking is completed in the last time slot TS3 ofthis cycle C1, and the packet is stored into the buffer TB by settingthe transmission switch T to the cross state. It is understood thatswitch cross states are shown with a cross, i.e., “X,” and bar statesare shown by opposing bars, i.e., “_(—) ⁻.” A packet is stored as longas the transmit switch T is in the bar state, and is transmitted to thenetwork by setting the transmit and optical switches T, S to the crossstates 2W (6) time slots after the reservation TS6. Whenever, such as atthe third time slot TS3, the node recognizes a packet with its address,the node stores the packet 2W time slots later TS9 by setting theoptical and receive switches S, R in the cross states. The node startsunstacking the packet at the beginning of the next cycle TS10 bymaintaining the receive switch R in the cross state.

FIG. 4 shows an alternative transmit switch T′ for a packet-switchedring network in accordance with the present invention. It is understoodthat an alternative receive (R′) switch can have the same configurationas the transmit switch T′. The transmit switch T′ includes a rapidlytunable delay line (RTDL) having log₂W stages, each of which comprises arespective 2×2 optical switch OS1-OSlog₂W followed by an optical delayline D1-Dlog₂W. The delay of the ith stage is D_(i)=WT_(p)/2^(i). Thetotal delay through the RTDL can range from T_(p) to WT_(p) in theincrements of T_(p) by setting 2×2 switches to the appropriate states.

Each packet is stacked and transmitted through the RTDL in the lastframe of a cycle, and leaves the RTDL to enter the ring network byputting switch S (FIG. 2) in the cross state exactly two cycles after ithas been announced on the control channel, as shown in FIG. 3. On theother side, the packet is received from the ring by putting switch S inthe cross state exactly two cycles after its announcement, and delayedthrough the RTDL until the beginning of the next cycle when it isunstacked.

It is understood that the switches T, R, S are fully coordinated. Inother words, transmitted and received packets do not require oppositesetups of the switches in the same time slot. The transmit switch T hasto be in the bar state only while it stores a packet prior to itstransmission and there can be only one such packet. The bar state forthe transmission switch T is only required up to the last slot of thecycle, which is before it might have to be switched to the cross statein order to store a new packet. Similarly, switch R must be in the barstate only while it stores the received packet until the beginning ofthe next cycle. So, the bar state of switch R will end before it mighthave to be switched to the cross state in order to store a new receivedpacket in the next cycle. In addition, no packets will be sent from atransmitter over point B (FIG. 2) to be unstacked in the receiver. Apacket is possibly present at point A (FIG. 2) only in the last timeslot of a cycle, and in this case it is stored by setting T into thecross state.

In general, the nodes renew their credits once per frame period, i.e.they load their counters with the negotiated numbers of creditsc_(ij)=a_(ij); 1≦i, j≦N at the beginning of each frame. It is understoodthat only a queue with positive counters can make a reservation, and itscounter c_(ij) is decremented by 1. The queues and credit allocationsare examined to start a new frame when each queue is either empty or isout of credits as set forth below in Equation 1:

$\begin{matrix}{{I = {{\sum\limits_{i,j}{q_{ij} \cdot c_{ij}}} = 0}},} & {{Eq}.\mspace{14mu} (1)}\end{matrix}$

where q_(ij) is the number of packets in queue (i,j), and c_(ij) is thenumber of credits in each queue. Note that some node source-destinationpairs may not use their credits if they do not have enough traffic. Inthat case, frames will shorten (l=0 before the end of the frame) andother source-destination pairs will get credits more often, i.e., sharethe excess bandwidth.

In an illustrative embodiment, an admission controller is placed at agiven node for analyzing whether newly requested bandwidths can beallocated to the particular source-destination pair. More particularly,the admission controller calculates if the MAC protocol ensures Δ a_(ij)new credits to the node pair (i,j) in each frame (which is no longerthan F_(max) time slots) for the existing credit allocation a_(kl), 1≦k,l≦N, where N is the number of nodes.

The network architecture and MAC protocol ensure a_(ij)>0 time slots tonode source-destination pair (i, j), 1≦i, j≦N, within a frame of length≦F_(max), if the conditions expressed in Equation 2 below are satisfied:

$\begin{matrix}{{{W \cdot ( {{\sum\limits_{l}a_{il}} + {\sum\limits_{k}a_{kj}}} )} + {\sum\limits_{\underset{karrow{iarrow l}}{k,l}}a_{kl}}} \leq {F_{\max}.}} & {{Eq}.\mspace{14mu} (2)}\end{matrix}$

where k, l, k→i→l are nodes such that node k transmits packets to node lover node i, and a_(il), a_(kj), and a_(kl) represent the respectivetime slots assigned to the node source-destination pair. The creditsassociated with the source node (i) and the destination node (j) aremultiplied by the number of wavelengths W due to time required forstacking and unstacking the composite packet. That is, as describedabove in conjunction with FIG. 3, each time slot 300 is grouped incycles of length W so that each node can transmit and receive at mostone packet within each cycle 302. In general, Equation 2 examines thecredits already assigned to the source node (i), the destination node(j), and nodes (l) passing packets from the source node (i) to determineif there is sufficient remaining bandwidth to accommodate the requestedadditional bandwidth.

For example, if t_(max) is the last time slot assigned tosource-destination pair (i, j), which is in cycle F_(max), in any cyclef≦F_(max), either node i transmits a packet or node j receives a packet,or all time slots are busy when passing node i. If there is an emptyslot in cycle f≦F_(max), and destination node j is not reserved, node ireserves it because node i still has unused credits. There are at mostΣ_(l≠j)α_(il)+Σ_(k≠i)α_(kj)+α_(ij)−1 cycles before F_(max) in whicheither source i or destination j are busy. These cycles occupy at mostW(Σ_(l≠j)a_(il)+Σk≠ia_(kj)+a_(ij)−1) time slots. That is, the cycles areno more than the sum of the number of credits assigned to anotherdestination node, i.e., not node j, the credits assigned to source nodeother than node i, and the credits already assigned tosource-destination node pair i,j. The remainder of the cycles that arefully occupied comprise at most

$\sum\limits_{\underset{karrow{iarrow l}}{k,l}}a_{kl}$

time slots. As shown in Equation 3 below, the system determines whetherthe sums of these cycles are less than the last time slot in the frame:

$\begin{matrix}{{t_{\max} \leq {{\cdot W \cdot ( {{\sum\limits_{l \neq j}a_{il}} + {\sum\limits_{k \neq i}a_{kj}} + a_{ij} - 1} )} + {\sum\limits_{\underset{karrow{iarrow l}}{k,l}}a_{kl}}}};} & {{Eq}.\mspace{14mu} (3)}\end{matrix}$

where k,l k→i→l are nodes such that node k transmits packets to node lover node i as described above. If this equation is satisfied, thent_(max)<F_(max) and source-destination pair (i, j) will use all assignedcredits in less than F_(max) time slots.

It is understood that the below implementation of Equation (2) providescomputational simplicity as well as parallel processing when determiningwhether to accept new bandwidth requests.

A controller node stores the following: the number of credits assignedto each source-destination pair (k, l) (a_(kl)), the number of creditsassigned to each source s_(k)=Σ_(m)a_(km) the number of credits assignedto each destination d_(l)=Σ_(n)a_(nl), the number of credits assigned tonode pairs with node k in between

${l_{k} = {\sum\limits_{\underset{marrow{karrow n}}{m,n}}a_{mn}}},$

and the maximum number of credits assigned to destinations addressed bynode k is D_(k)=max a_(kl>0)d_(l), i.e., the most heavily loadedreceiver. When new bandwidth Δ a_(ij) is requested, it is allocated ifthe conditions specified in Equation 4 below are satisfied:

$\begin{matrix}{{{{W \cdot ( {s_{k}^{\prime} + D_{k}^{\prime}} )} + l_{k}^{\prime}} \leq {F_{\max,}1} \leq k \leq N},{{where}\text{:}}} & {{Eq}.\mspace{14mu} (4)} \\{{a_{ij}^{\prime} = {{a_{ij} + {\Delta \; a_{{ij},}\mspace{14mu} s_{i}^{\prime}}} = {{s_{i} + {\Delta \; a_{{ij},}\mspace{14mu} d_{j}^{\prime}}} = {d_{j}^{\prime} + {\Delta \; a_{{ij},}}}}}}{{a_{kl}^{\prime} = a_{kl}},{s_{k}^{\prime} = {{s_{k} \cdot d_{l}^{\prime}} = d_{l}}},{1 \leq k},{l \leq N},{k \neq i},{l \neq j},}} & {{Eq}.\mspace{14mu} (5)} \\{l_{k}^{\prime} = \{ \begin{matrix}{l_{k} + {\Delta \; a_{ij}}} & \vdots &  iarrow karrow j   \\l_{k} & \vdots & {otherwise}\end{matrix} } & {{Eq}.\mspace{14mu} (6)} \\{D_{k}^{\prime} = \{ \begin{matrix}{\max ( {D_{k},d_{j}^{\prime}} )} & \vdots & {a_{kj}^{\prime} > 0} \\D_{k} & \vdots & {otherwise}\end{matrix} } & {{Eq}.\mspace{14mu} (7)}\end{matrix}$

If the new request is accepted, the parameters of interest are updateda_(ij)←a′_(ij), s_(i)←s′_(i), d_(j)←d′_(j), l_(k)←l′_(k), D_(k)←D′_(k),1≦k≦N. Note that comparisons and additions in Equations 5, 6, and 7 canbe done in parallel for all nodes such that the time complexity of thealgorithm is in the first order O(1).

In general, for uniform traffic each source-destination pair gets thesame number of credits, and each link is equally loaded. The inequalitydefined in Equation 4 can be rewritten in Equation 8 as follows:

2ρ_(T)+ρ_(L)−1  Eq. (8)

where ρ_(T)=W·Σ_(l)a_(il)/F_(max) is the transmitter utilization, and

$\rho_{L} = {\sum\limits_{\underset{karrow{iarrow l}}{k,l}}{a_{kl}/F_{\max}}}$

is the link utilization. Since a packet passes N/2 nodes on average, theaverage number of packets transmitted through the network isρ_(L)N/(N/2)=2ρ_(L). Packets are transmitted at the bit-rate of WB,where B is the laser bit-rate. So, the average network throughput is2ρ_(L)WB. The average network throughput is also equal to the sum ofaverage bit-rates that nodes generate, which is ρ_(T)NB. Thus it followsthat the throughput can be expressed below in Equation 9:

2ρ_(L) WB=ρ _(L) NB

ρ _(L) =Nρ _(L)/2W,  Eq. (9)

From the inequalities expressed above, the resulting inequalitiesdescribed in Equations 10a,b can be obtained:

$\begin{matrix}{\rho_{T} \leq {\frac{1}{2 + {N/( {2\; W} )}}\mspace{14mu} {and}\mspace{14mu} \rho_{L}} \leq {\frac{1}{1 + {4\; {W/N}}}.}} & {{Eq}.\mspace{14mu} ( {{10\; a},b} )}\end{matrix}$

The guaranteed transmitter and link utilization for different node towavelength ratios N/W is given in Table 1 below

TABLE 1 Transmitter and link utilization [%] N/W 1 2 4 8 16 ρ_(T) 40 3325 17 10 ρ_(L) 20 33 50 66 80

The transmitter utilization decreases approaching 2W/N as the number ofnodes per wavelength increases since each node gets the smaller portionof the laser bit-rate. Also, the link utilization increases approaching100% as the number of nodes per wavelength increases showing thebenefits of the statistical multiplexing.

At initialization, nodes negotiate the maximum frame length, e.g.,F_(max) time slots. Credit negotiation is well known to one of ordinaryskill in the art. A credit of one time slot per frame guarantees to theparticular queue a bandwidth granularity G that can be expressed as setforth below in Equation 12:

G=W·B/F _(max),  Eq. (12)

where B is the laser bit-rate, and W is the number of differentwavelengths. Bandwidth can be reallocated in an access time determinedby the frame duration A as defined in Equation 13 below:

A=F_(max)T_(p).  Eq. (13)

where Tp is the time slot duration. The frame duration (or access time)should be sufficiently long to provide fine traffic granularity G, butshort enough to respond to the fast traffic changes with relativelyshort access time A. Assuming for example, W=30, B=10 Gbps, T_(p)=50 ns,and F_(max)=10⁶, a network provides a total capacity of WB=300 Gbps, agranularity G=0.3 Mbps, and an access time A=50 ms. Even in ahigh-capacity network with W=100 wavelengths and throughput of WB=1Tbps, fine granularity, e.g., G=1 Mbps, and short access time, e.g.,A=50 ms, are provided.

Due to the fine granularity and the fast access time, the network easilysupports web browsing, streaming, and other dynamic applications thatare dominant in data networks. Since a tunable laser can potentiallytransmit at the bit-rate of 10, each node can serve thousands ofbroadband end-users.

As described above, there is a trade-off between traffic granularity andaccess time. For a fixed access time which is demanded by an applicationrequirement, the traffic granularity (the minimum bandwidth that can bereserved) can be decreased only by decreasing the total networkcapacity. In one embodiment, different portions of the network capacityare pre-allocated to different groups of applications according to theirbandwidth requirements. This arrangement simplifies the network controland utilizes the resources more efficiently.

The network architecture shown and described above naturally supportsapplications like web-browsing and video-streaming since it can providea granularity of about 1 Mpbs and an access time of about 50 ms, for thetotal switching capacity of 1 Tbps. However, some applications such asvoice, video-conferencing, audio-streaming etc. require much finergranularity. Finer granularity can be achieved by multiplexing trafficat the edge of the network. For example, one composite packet cancomprise multiple packets carrying different applications between aparticular source-destination pair. If there is not enough trafficbetween some source-destination pairs, assigned bandwidth isunderutilized. Alternatively, different portions of bandwidth can beappropriately pre-allocated to different services in order to achieveefficient utilization.

From Equation 2 above, the granularity for the given network capacitycan be decreased by increasing the frame length. But then, the accesstime is increased according to Equation 3. The tuning time of fasttunable lasers is roughly about 10 ns, and the packet slot should bemuch longer than the tuning time, e.g. T_(p)>50 ns. On the other side,interactive communications such as telephone calls and videoconferencing require access times which are A<100 ms. Such a shortaccess time is desirable for other applications as well. From theseobservations and Equation 3, it follows that the frame length should beF_(max)<10⁶. So, in the network with a terabit switching capacity,granularity is G>1 Tbps/10⁶=1 Mbps as calculated from Equation 2.Granularity can be also decreased by decreasing the network capacity,i.e. the number of wavelengths. It is understood thatlow-bandwidth-demanding applications require finer granularity, but atthe same time a smaller network capacity. Voice requires a bit-rate ofseveral kbps, video-conferencing and audio-streaming require severalhundreds kbps, while web browsing and video-streaming require severalMbps. Consequently, it may be desirable to assign W₁ wavelengths tovoice and control packets, W₂ wavelengths to video-conferencing andaudio-streaming and W₃ wavelengths for web-browsing and video-streaming.Here, W₃≈10W₂≈100W₁.

As shown in FIG. 5, these three groups of applications can be integratedin a packet-switched ring network, such as the network described above.Different services are transported on three different sets ofwavelengths Λ₁, Λ₂, Λ₃. Each node 400 includes first and secondwavelength multiplexers 402, 404 and first and second wavelengthdemultiplexers 406, 408. First, second, and third switches 410, 412, 414are coupled to the multiplexers and demultiplexers 402, 404, 406, 408 asshown. And a transceiver 416 is disposed between the second multiplexer404 and the second demultiplexer 408.

The wavelength demultiplexers 406, 408 separate the three sets ofwavelengths Λ₁, Λ₂, Λ₃ so that they can be selectively added and droppedat each node. A node can selectively drop and add any set of wavelengthsby setting the appropriate (2×2) optical switch 410, 412, 414. A tunablelaser (not shown) transmits only those wavelengths that are to be added,and these wavelengths are stacked. After the switching, wavelengths arecombined by the wavelength multiplexers 402, 404. Only droppedwavelengths are unstacked.

Nodes make reservations on the control channel independently fordifferent services. Also, MAC and admission control protocols areexecuted independently. Therefore, the granularity for thisconfiguration is defined in Equation 14 and the access time for theseservices is defined in Equation 15 below:

G ₁ =W ₁ ·B/F ₁ , G ₂ =W ₂ ·B/F ₂ , G ₃ =W ₃ ·B/F ₃,  Eq. (14)

A ₁ =F ₁ ·T _(p) , A ₂ =F ₂ ·T _(p) , A ₃ =F ₃ ·T _(p).  Eq. (15)

For example, assuming W₁=1; W₂=10, W₃=100, B=10 Gbps, T_(p)=50 ns, andF₁=F₂=F₃=10⁶, the network provides services with different granularitiesof G₁=10 kbps, G₂=100 kbps and G₃=1 Mbps, and fast access times ofA₁=A₂=A₃=50 ms.

The separation of the services follows from the severe variations of thebandwidth requirements for different applications. The portion of thenetwork capacity used for low-bandwidth applications is negligible, andcan be pre-allocated. Otherwise, mismatch of the granularities in thenetwork with integrated services can easily cause bandwidthunder-utilization, e.g., assigning one credit that guarantees 1 Mbps toone telephone call requiring 10 kbps is undesirable bandwidth waste.Note also that the node complexity is only slightly increased by theservice separation since all services share most of the optical devicesat the node.

In one embodiment, best effort traffic transmission is utilized by thenetwork. Best effort traffic refers to attempted transmission of packetsby a node not having sufficient assigned credits for the transmission.In general, the node makes a transmission attempt without reserved timeslots that can be either successful or unsuccessful. If unsuccessful,the transmission attempt is dropped.

It is understood that various modifications can be made to theabove-described embodiments without departing from the presentinvention. For example, user nodes can be equipped with rapidly tunabletransmitters and receivers. The transmitter and receivers can beattached to the ring network by the optical 2×2 coupler. Time can bedivided into slots, e.g., no cycles. Nodes observe the control channelto determine which wavelengths and receivers are available in the nexttime slot, and reserve one of the available wavelengths and receivers. Anode places the address of the reserved wavelength and receiver on thecontrol channel and observes if any of the packets is transmitted toitself and tunes to the wavelength of that packet. The above-describedMAC protocol and admission algorithm can readily support thisarchitecture.

The present invention provides an architecture, MAC protocol andadmission control mechanism to flexibly utilize a high-capacitypacket-switched ring network. Wavelength stacking and unstackingsimplifies the network control since it avoids fixed allocation of thewavelengths. A node makes reservations on the control channel, andlearns about the existing reservation from the control channel. It doesnot reserve any output that has been already reserved in the currentcycle of W time slots. Nodes are guaranteed negotiated shares of thering capacity by using credits. A node can make reservations within aframe as long as it has credits, so that each node is guaranteed anegotiated number of credits within the specified maximum frame length.Admission of new bandwidth request depends only on the utilization ofnodes and links in the network requiring minimal time complexity on theorder of O(1).

One skilled in the art will appreciate further features and advantagesof the invention based on the above-described embodiments. Accordingly,the invention is not to be limited by what has been particularly shownand described, except as indicated by the appended claims. Allpublications and references cited herein are expressly incorporatedherein by reference in their entirety.

1. A ring network, comprising: a node including: an optical switchcoupled to a fiber of the ring network; a transmit switch coupled to theoptical switch; a wavelength stacking assembly coupled to the transmitswitch for aligning in time packets of varying wavelengths created by atunable laser via a bank of delay lines; a receive switch coupled to theoptical switch; and a wavelength unstacking assembly coupled to thereceive switch.
 2. The ring network of claim 1, wherein the transmitswitch includes a buffer for storing packets, and the receive switchincludes a buffer for storing received packets.
 3. The ring network ofclaim 1, wherein the node performs a credit-based MAC protocol.
 4. Thering network of claim 3, wherein the node further includes an admissioncontroller for determining whether bandwidth requests are accepted basedupon an available frame capacity.
 5. A method for transmitting andreceiving packets on a ring network, comprising: stacking packets ofvarying wavelengths created by a tunable laser via a bank of delay linesto form a composite transmit data packet aligned in time; buffering thecomposite transmit data packet in a transmit switch; transmitting thecomposite transmit data packet onto the ring network via an opticalswitch; receiving a receive data packet via the optical switch;buffering the receive data packet in a receive switch; and unstackingthe receive data packet.
 6. The method of claim 5, further includingsetting the optical switch and the transmit switch to a cross state toput the composite transmit data packet on the ring network.
 7. Themethod of claim 5, further including setting the optical switch and thereceive switch to a cross state to obtain the receive data packet fromthe ring network.